(1) Field of the Invention
The present invention relates to a method for producing bonded articles, bonded articles and bonding agents.
(2) Related Art Statement
As optical bonding agents, organic bonding agents such as epoxy resin or acrylic resin and inorganic bonding agents such as low-melting point glass have been generally known. On the other hand, diffusion bonding, press bonding, optical contacting, etc. have been known as bonding methods using no bonding agents.
In Shin-gaku Giho, xe2x80x9cTECHNICAL REPORT OF IEICE US95-24: EMD 95-20: CPM95-32 (1995-07)xe2x80x9d, pp. 31-38, it is described that a substrate of lithium niobate was directly bonded to another substrate of lithium tantalate, and an optical waveguide structure was made by trial by thinning the lithium niobate substrate. This relates to the direct bonding between the substrates by utilizing molecular forces of hydroxyl groups adsorbed onto the surfaces thereof.
However, when a general bonding agent is used, it is difficult to obtain a bonded article having an extremely thin bonding layer. In case of the diffusion bonding, press bonding, optical contacting, etc. which use no bonding agents, it may be that substrates are not bonded or the bonding strength is low, if fine unevenness exists at bonding surfaces of the substrates to be bonded. On the other hand, a bonding layer can be made thin in a method of forming a thin film of low melting point glass on a surface of at least one of the substrates to be bonded, and contacting and heating the substrate surfaces. However, if fine unevenness exists at the surfaces of the substrates to be bonded, it may be also that they are not bonded together or the bonding strength conspicuously decreases.
It is an object of the present invention to provide a novel bonding method and a novel bonding agent, which can form a thin bonding layer and can assuredly realize desired bonding strength even if fine unevenness exists at surface(s) of substrates to be bonded.
The present invention relates to the method for producing a bonded article comprising a first substrate, a second substrate, and a bonding layer through which the first and second substrates are bonded. The method includes the steps of interposing a water-based bonding agent between the first and second substrates, and forming the bonding layer by heating the water-based bonding agent. The water-based bonding agent includes an alkali metal element and has a water-soluble compound dissolved therein. The water-soluble compound produces a composite oxide upon heating. Any combination of features recited in the dependent method claims are also considered preferred according to the present invention, unless contrary to the claimed invention.
The present invention also relates to a bonded article obtained using the above method.
The present invention further relates to the water-based bonding agent including an alkali metal element, a water-soluble compound which produces a composite oxide by heating, and water into which the water-soluble compound is dissolved. Any combination of features recited in the dependent bonding agent claims are also considered preferred according to the present invention, unless contrary to the claimed invention.
These and other objects, features and advantages of the invention will be apparent from the following description of the invention when taken in connection with the attached drawings, with the understanding that any modifications, changes and variations could be made by the skilled person in the art to which the invention pertains.